We investigated the seasonal occurrence, growth, age, and life history of Aurelia aurita in the Taniyama area of Kagoshima Bay, also some of the environmental factors such as the specific gravity, pH and the temperature, influence the appearance of Aurelia aurita in the surface layer. The size of an individual depends on environmental factors. In contrast the number of branching points of radial water vascular canals increasing with time, independently of environmental factors, and therefore could be used as an age index. By using age index, the population of Aurelia aurita sampled may consist a mixture of two cohorts. The assumption may be that the life span of Aurelia aurita is up to two years. By examining all stages of the life history of Aurelia aurita in Kagoshima Bay and comparing it with that of other locatives, it is found that the life form of Aurelia varies with their environmental circumstances. We suggest that how the habitat influence the life history in Aurelia should now be reviewed.